Guys, all this talk of moisture, temp/dewpoint spread, etc is confusing and completely unecessary information overload for a student about to undertake his first solo XC.
The simple answer is icing will not occur so long as you avoid clouds/mist/fog. Given that students have to avoid all 3 anyway this shouldn't be an issue.
Never heard of rain ice then? Relatively (and thankfully) quite rare in UK but by far the most dangerous of all to light aircraft and helicopters.
Falling rain occurs from a relatively warm layer of air, lying above a cold sector. The precipitation becomes supercooled as it falls then finds your cold aircraft toodling along below as a freezing "nucleus".... nasty!
I cancelled two days flying here in UK last winter because of forecast rain ice, so did the other operator I was supposed to be working with on the same job.
A true story to consider: About 25 years ago, in winter, an RAF Wessex helicopter was practicing underslung load work at RAF Gutersloh in Germany, hovering and flying low level circuits on the south side of the airfield. Suddenly, rain began to fall and clear ice began to form on the aircraft. The pilot terminated the training and asked for permission to return to dispersal, a couple of minutes hover taxying away. It didn't make it. The rain/clear ice built up so quickly that it was soon over it's max gross weight. Combined with the ice on the blades destroying lift it would no longer fly and it basically landed itself.
There was a photo of the front of the aircraft on the RAF incident report - scary stuff. Clear ice was encrusted inches deep, all over the helicopter.
I was based at Gutersloh sometime afterwards. One winter's day we walked to lunch, using the back path from the hangar through a small pine wood. Moderate to heavy rain began to fall from an encroaching warm front and it froze as it hit the ground, or anything else. Half an hour later, very large branches were being ripped off those pine trees by the sheer weight of the ice on them. Walking back to the hangar by the same route was almost impossible and highly dangerous!
Needless to say, all RAF flying for the day was cancelled.
If the OP needs further advice, he must obviously take it from his supervising instructor on the day of the flight.
